當(dāng)前的射頻識(shí)別(RFID)標(biāo)簽測試方法對(duì)大量的倉庫和貨架上的標(biāo)簽是一個(gè)負(fù)擔(dān),因?yàn)楫?dāng)前的測試方法需要對(duì)每一個(gè)標(biāo)簽獨(dú)立調(diào)諧,因此測試流水線化可以獲得更快的原型設(shè)計(jì)時(shí)間,喬治亞工學(xué)院的工程師們最近設(shè)計(jì)了一種新的測試機(jī),可以在新標(biāo)簽芯片仿真的時(shí)候同時(shí)測試數(shù)百個(gè)RFID標(biāo)簽。

喬治亞電氣和計(jì)算機(jī)學(xué)校的Gregory Durgin教授宣稱“我們?cè)O(shè)計(jì)了一種超靈活的系統(tǒng),能夠允許改變調(diào)制方法,載波頻率,射頻標(biāo)簽配置,天線類型?D?D任何可以使工程師獲得更大范圍和靈活性的系統(tǒng)性能參數(shù),一些公司已與我們合作運(yùn)用這一測試機(jī)來測試新的天線標(biāo)簽,并利用這些新的傳感器性能來刷新現(xiàn)有的RFID標(biāo)簽。”

RFID標(biāo)簽運(yùn)用十分廣泛,從存貨管理到收費(fèi)系統(tǒng)到護(hù)照識(shí)別再到行李跟蹤。而大部分的標(biāo)簽都只是被動(dòng)式的,包含一個(gè)芯片,一個(gè)能夠接收無信電信號(hào)的天線給附近的讀卡機(jī)提供身份識(shí)別。

RFID標(biāo)簽測試的最大的問題是測試量?D?D倉庫和商店貨架往往包含讀卡機(jī)范圍內(nèi)的上百種標(biāo)簽,很多標(biāo)簽隱藏在其他標(biāo)簽的后面,當(dāng)這些標(biāo)簽都在讀卡機(jī)范圍內(nèi)的時(shí)候,通常的協(xié)議是先響應(yīng)最強(qiáng)信號(hào)的標(biāo)簽,識(shí)別后讓它休眠再處理下一個(gè)最強(qiáng)信號(hào),這一系列過程很耗時(shí)。

然而,喬治亞測試機(jī)運(yùn)用了一種防干擾系統(tǒng)能夠同時(shí)傳輸若干獨(dú)立信號(hào),這個(gè)系統(tǒng)允許256個(gè)標(biāo)簽同時(shí)被訪問,而不是要求讀卡機(jī)依次訪問各個(gè)標(biāo)簽,喬治亞測試機(jī)可以與400平方英尺內(nèi)的RFID標(biāo)簽通信,同時(shí)收集標(biāo)簽信息,該系統(tǒng)還能實(shí)時(shí)追蹤它們的信號(hào)強(qiáng)度。

Durgin 說“我們有一個(gè)自動(dòng)機(jī)械配置系統(tǒng)可以自動(dòng)調(diào)整標(biāo)簽的距離,這樣我們可以研究空間變化和鏈接衰減的特征。”

用新天線設(shè)計(jì)測試RFID標(biāo)簽也有一個(gè)新問題,需要新的RFID標(biāo)簽的物理原型用來測試天線,往往也需要昂貴的ASIC設(shè)計(jì)。為解決這一問題,喬治亞的團(tuán)隊(duì)發(fā)明了一種替代品來替代新標(biāo)簽設(shè)計(jì)里的ASIC,從而使這種新的天線能夠很快被測試。

Durgin 說“我們用傳統(tǒng)的發(fā)收器硬件來產(chǎn)生和接收任意波形,這樣我們能迅速的測試獨(dú)立的天線配置和若干天線,而不需要為每一個(gè)實(shí)驗(yàn)創(chuàng)立新的標(biāo)簽。同時(shí),我們用定制的微波電路來模擬ASIC,用它可以模擬任意載頻和任意調(diào)制方法的真實(shí)的RFID標(biāo)簽,甚至是全新的設(shè)計(jì)”

目前測試機(jī)僅限于915MHz的測試,這也是被動(dòng)式RFID應(yīng)用的最常用的頻率,但目前已被更新至2.4- 5.7-GHz。這些更高的頻率將使標(biāo)簽可以用更小的天線實(shí)現(xiàn)更廣泛的操作范圍。

喬治亞RFID測試機(jī)由國家科學(xué)基金會(huì)贊助。喬治亞工學(xué)院工程學(xué)研究生Anil Rohatgi 和 Joshua Griffin主導(dǎo)這項(xiàng)研究。

翻頁查看英文原文:

Test bed streamlines RFID development

RFID tags flooding warehouses and product shelves tax current testing methods, which separately tune into each tag. To streamline testing while enabling rapid prototyping of new designs, Georgia Institute of Technology engineers have crafted a new test bed they say is capable of simultaneously testing hundreds of RFID tags while emulating the chip in a new tag design.

"We have designed a super-flexible system that allows us to vary modulation scheme, carrier frequency, RF tag configuration, antenna types -- anything an engineer can dream up for making these systems perform with greater range and reliability," claimed professor Gregory Durgin at Georgia Tech's School of Electrical and Computer Engineering. "Companies have already -partnered with us to use the testbed to test new tag antennas, and to retrofit existing RFID tags with new sensor capabilities."

RFID tags are used for everything from inventory management to toll collection to passport identification to tracking luggage. Most tags are passive, including a chip and an antenna that absorbs a radio signal to backscatter its identity to a nearby reader.

The biggest problem with testing RFID tags is the sheer volume--warehouses and store shelves often contain hundreds of tags within range of a reader, many hidden behind other tags. When multiple tags are within range of a reader, the usual protocol is to interrogate the tag with the strongest signal, then put it to sleep and proceed on to the next strongest signal. That serial process can be time consuming.

Instead, the Georgia Tech test bed uses an anti-collision system capable of transmitting multiple, unique signals. The system allows up to 256 tags to be interrogated simultaneously. Instead of requiring readers to be within about a foot of tags, the Georgia Tech test bed can communicate with RFID tags within 400 square feet of the tester. Along with collecting tag information, the system can also track their signal strength in real time.

"We also have a robotic positioning system that drags tags through space so that we can study spatial variability and characterize link fading," said Durgin.

Testing RFID tags with new antenna designs is also a problem. A physical prototype of the new RFID tag must be built to test the antenna, often involving the costly ASIC fabrication. To solve the problem, the Georgia Tech team created an emulator that substitutes for the ASIC in a new tag design, thus allowing new antennas to be quickly prototyped and tested.

"We use custom transmitter and receiver hardware to generate and receive an arbitrary waveform of our own design so we can rapidly test unique antenna configurations and multiple antennas without actually constructing new tags for each experiment," said Durgin. "Instead, we use our custom microwave circuits to emulate the presence of an ASIC--it just clips onto the antenna. With it, we can emulate realistic RFID tags at any carrier frequency with any modulation scheme--even new ones of our own design."

The current test bed is limited to measurements at 915 MHz, the most common frequency for backscatter RFID applications, but it is currently being upgraded to test antennas at frequencies of 2.4- and 5.7-GHz. These higher frequencies will enable tags to operate over wider ranges while using smaller antennas.

The Georgia Tech RFID test bed was funded by the National Science Foundation. Georgia Tech engineering graduate students Anil Rohatgi and Joshua Griffin conducted the research.